Methemoglobin Formation After Administration of Hemoglobin Conjugated to Carboxylate Dextran in Guinea Pigs. Attempts to Prevent the Oxidation of Hemoglobin

Abstract

In 1990, McGown demonstrated in vitro a limitation of extracellular methemoglobin (metHb) formation by releasing and recycling of ascorbic acid by red blood cells [1]. In order to investigate the autoxidation of free or modified hemoglobin in plasma and the possibility of reproducing McGown's phenomenon in vivo, we performed a 50% blood mass exchange in guinea-pigs with a 70±5 g/1 dex-BTC-Hb solution (metHb < 5%). Methemoglobin was determined according to Evelyn-Malloy's method. We observed a clear but limited oxidation of plasmatic hemoglobin (MetHb∼30–40% at t = 12hrs up to t = 24hrs). A similar blood mass exchange was performed with the same hemoglobin solution which was previously totally oxidized into metHb. 40% of this methemoglobin was found to be reduced after 12hrs. These results demonstrated a marked reducing activity by residual blood as shown by others [2], The addition of potentially protective compounds such as ascorbic acid (non enzymatic intraerythrocytar reduction pathway), methylene blue or riboflavin (enzymatic intraerythrocytar pathway), allowed a significant drop in the methemoglobin level. On the contrary, we didn't observe any reducing effect with reduced glutathione.